The present invention relates to a method for ensuring safe or reliable operation of a programmable automatic control device intended to control a user device such as a machine or a plant and an automatic control device for carrying out the said method.
There are already known programmable automatic control devices which are so designed that a simple failure of any component thereof places the outputs of the automatic control device into a predetermined state. However, the known automatic control devices of this type are designed in the form of a system redundant in space, i.e., in the form of a duplicated system. They suffer from the major disadvantage of being expensive and difficult to use and to program.
The present invention has as its purpose to provide to the problem relating to the programmable automatic control devices a solution which allows fulfilling the same safety or reliability functions as the known automatic control devices, but at a lower cost.
To achieve this purpose, the present invention provides a method for ensuring safe or reliable operation of a programmable automatic control device, which is characterized in that, for a same given state of the inputs of the automatic control device, a same processing unit such as a microprocessor is caused to execute the same program successively twice by using every time another bus, and use is made as a criterion of correct operation of the automatic control device the identity of the two signals resulting from the two successive executions of the program.